Vol. 54.] MISS J. DONALD ON THE GENUS ACLISINA. 53 



retain the name tenuis for them and the small Belgian shells which 

 were originally so called, and to regard them as a distinct variety 

 ■of A. pulchra. 



The contour of the whorls varies in different individuals, some, 

 especially those with coarser ornamenting threads, being more 

 angular than others with finer threads. The spiral angle also 

 shows a considerable amount of variation, so much so that the 

 two extremes without the intervening forms might be regarded as 

 distinct species. 



Two or three small specimens from Swindridge and one from 

 Law vary so markedly, in being much more slender, that they 

 appear to constitute a distinct variety, for which 1 would suggest the 

 varietal name intermedia. They are immature, but if fully grown 

 it is unlikely that the spiral angle would equal that of the type. 

 They are intermediate in form between A. pulchra and A. costatula. 



Resemblances. — This species somewhat resembles Adisoides stria- 

 tula, but it is more robust, the whorls are generally more angular, 

 there is no slit in the outer lip, and the form of the protoconch is 

 different. It is also like Loxonema sulcatula, M'Coy,^ but it is 

 difficult to make a just comparison with that species as it is only 

 represented by three imperfect external moulds. The ornamenta- 

 tion and form of the protoconch are very similar to those of 

 A. costatula ; but the latter has not the numerous additional threads 

 on the body-whorl, and it is also much more slender. 



Dimensions. — As before stated, the Belgian type of this species 

 is much larger than the Scottish examples; it has seven whorls 

 preserved, whose length := 12 mm. The specimen belonging to 

 M. de Dorlodot has ten whorls in a length of 13| mm. The 

 type of Murchisonia tenuis has eight whorls in a length of 8 mm. 

 The most perfect Scottish specimen (PI. Ill, fig. 1) that I have seen 

 consists of ten whorls, its length = 7 mm., width = 2 mm. It is 

 from Swindridge, and is in the collection of Mr. James Thomson. 

 The shell represented in PI. Ill, fig. 2, consists of seven and a half 

 whorls in a length of 4^ mm., its width = nearly 2 mm. It is 

 from Robroyston and is in the collection of Mr. Neilson. Another 

 individual with greater spiral angle and fewer and stronger orna- 

 menting threads is in my own collection from Craigenglen ; it has 

 fi.ve whorls in a length of 3 mm., and its width = 1 J mm. (PI. Ill, 

 fig. 2 a). Other examples would be larger if entire. 



The variety intermedia from Law is in Mr. Bennie's collection ; 

 it consists of eight whorls besides the protoconch, its length = 

 2| mm., width = about | mm. (PI. Ill, figs. 5 & 5 a). A specimen of 

 this variety from Swindridge has the protoconch larger and more 

 orbicular than usual. 



Locality and Horizon. — This species has a wide range, occurring 

 in the Calciferous Sandstone Series (cZ^) at Itanderstone, Fife; in 

 the Lower Limestone Series (d'^) at Craigenglen and at Law, Dairy, 

 and in the Upper Limestone Series {d^) at Swindridge ; Raesgill, 



1 ' Syn. Char. Garb. Foss. Irel.' 1844, p. 30 & pi. v, fig. 6. 



